Coucou,
B= (2x + 1)(3x - 8) + (6x+7)(3x-8)
= (2x * 3x + 2x * -8 + 1* 3x + 1 * -8) + (6x*3x + 6x * -8 + 7* 3x + 7* -8)
= ( 6x² -16x + 3x -8) + ( 18x² -48x + 21x - 56)
essaie de continuer, tu as juste a mettre les termes ensembles
A = 12x^3 - 6x^4 + 18x
exemple : 6x^4 - 18x^3 + 12x^2 = 2x^2(3x^2 - 9x + 6x)